June 17, 1997 Web posted at: 10:46 p.m. EDT (0246 GMT) ATLANTA (CNN) -- A byproduct of chlorination in drinking water has been linked to cancer in rats, leading the government to investigate adverse effects of water disinfectants. A chemical byproduct called MX develops from organic compounds in the chlorinated drinking water, and Finnish researchers found that rats exposed to high levels of MX got several types of cancer. "The new study is showing that yet another one of the common byproducts of using chlorine in our drinking water appears to be linked to cancer," said Erik Olson of the National Resources Defense Council. The researchers report their findings in the Journal of the National Cancer Institute, to be published Wednesday. "Although these findings cannot be extrapolated to humans, MX should be studied as a candidate risk factor" in the consumption of chlorinated drinking water, the study says. Scientists in the National Toxicology Program, under the auspices of the National Institutes of Health, are launching a two-year study of MX and other chlorination byproducts. They want to see how MX -- at various low doses -- affects the occurrence of cancer in rats and mice. MX a potent carcinogen in rats In the Finnish study, government and university scientists fed groups of 50 rats three different dosages of MX in drinking water. The 50 rats in a fourth group received no MX and were maintained as a control. At the end of two years, the rats were killed and their body tissues were analyzed. Among rats receiving the highest doses of MX, more than half developed cancer or tumors of the thyroid, compared to about 22 percent in the control rats. The MX rats also developed cancer of the lungs, skin, breast, liver and pancreas. "MX is a potent carcinogen in both male and female rats, and it causes tumors at doses that are not overtly toxic to rats," the Finnish researchers reported. The cancer potency of MX is up to 170 times greater than some other chemical byproducts in chlorinated water, such as chloroform and bromodichloromethane, according to Dr. Ronald Melnick of the National Institute of Environmental Health Sciences. However, he said the Finnish researchers used a dosage of MX thousands of times higher than what is present in the typical U.S. water system that is treated with chlorine. He estimated that MX at the doses studied in Finland would cause about two cancers per 1 million people over a lifetime. Benefits of chlorine outweigh risks Melnick said although MX should be studied, there should be no move to remove chlorination from public drinking water. Chlorination controls many waterborne diseases, including typhoid fever, cholera and dysentery. When chlorination was stopped recently in Peru, for instance, there was a cholera epidemic of 300,000 cases. More than 90 percent of drinking water in the United States is treated to remove harmful bacteria, and the benefits far outweigh the known cancer risks, scientists say. But MX levels in U.S. drinking water are not usually monitored routinely, and Melnick said that is needed. "We want our water to be as safe as possible, but in a chemical treatment such as this, it is impossible to have absolute zero risk," he said. The presence of MX in drinking water may be controlled by filtering the water before the chlorine is added, Melnick said. Such filtering would remove the organic compounds that chlorine acts on to produce MX. For those wishing to try to lessen any risk at home, experts say a good activated charcoal filter can trap some of the potential carcinogens in tap water. |